The leaching of constituents from particlized mineral materials is practiced utilizing a wide variety of materials and equipment. Leaching procedures are particularly useful for the recovery of metals from particulized mineral ores, such as gold and silver ores. The dominant process for the extraction of such metals from ores is leaching with alkaline cyanide solution and oxygen, and this basic procedure has changed relatively little since the issuance of the first patent thereon in 1887. Despite extensive use of cyanide leaching, however, it has a number of drawbacks associated therewith, including the practical necessity of either grinding the ore fine for continuous agitation leaching or utilizing batch leaching methods on coarser material, significant pollution loads, and minimal adaptability.
According to the present invention a method for the leaching of particlized mineral materials to remove constituents therefrom is provided which has enhanced effectiveness compared to prior art procedures. The method according to the invention is particularly applicable to the removal of metals from metal bearing ores, such as gold and silver ores, but also is adaptable to other processes, such as the removal of the pyritic, organic, and sulfate sulfur compounds present in a solid carbonaceous fuel of the coal or coke type.
The method according to the invention effects the treatment of a slurry of particlized mineral material in a continuous manner, with no large pressure losses and with good metal removal efficiency. The process is capable of treating particlized mineral materials in a continuous manner even when there is a relatively large percentage of small fines (e.g. 200 mesh or below), without channelling and with excellent uniformity of flow. The process according to the invention is easily adaptable to high temperature and/or high pressure conditions, and may be closed to the atmosphere thereby reducing the pollution potential associated therewith. The process also generally requires less grinding equipment and energy and less pumping, agitating, and like energy expenditures compared to prior art continuous leaching processes, can handle ores of a wide variety of sizes, and can handle soft materials--such coke or coal.
Further, by practicing the invention substantially the same results can be achieved as by leaching with carbon added to the "pulp" being leached, without the necessity of adding carbon. This is in part because the retention time for the dissolved metal (e.g. gold) in contact with ore is very short due to countercurrent flow in the reactor vessel of the invention.
The invention also comprises a novel slurry of particlized mineral material, and a method of removing metals from a pregnant leaching solution utilizing a conventional carbon adsorber device.
According to one aspect of the present invention, a particlized mineral material, such as gold or silver ore, is slurried with a liquid. The material is passed downwardly in a generally vertically upstanding leaching reactor vessel, and leaching liquid is passed counter-currently (i.e. upwardly) to the continuously downwardly passing slurry. Treated slurry is continuously removed from a bottom portion of the vessel, while pregnant leaching liquid (with leached constituents, e.g. gold or silver) is continuously removed from the top of the vessel, as by utilizing a stilling well. The leached slurry is continuously washed, preferably in a single stage or in a two stage wash procedure utilizing a vessel or vessels comparable to the leaching reactor. For two stage washing, the spent wash liquid from the first stage of the washing is utilized as the liquid for slurrying the particulized mineral material.
In order to lock the ore particles in a stable network for treatment in the continuous process according to the invention, a flocculating agent and fibers are added to the liquid and particulized mineral material during slurrying thereof. Any suitable conventional flocculant, such as synthetic polymers, may be utilized, and the fibers may be selected from cellulosic fibers (e.g wood pulp fibers), fiberglass fibers, or ceramic fibers.
The utilization of flocculants and fibers is not restricted to the practice of a continuous process. Rather the formation of a slurry utilizing those materials is also applicable to batch leaching and washing operations, and the like.
The cyanide solution leaching liquid, containing metals removed from particlized ores, is treated in a particular manner to facilitate removal of the metal therefrom. The pregnant leaching solution--that removed from the top of the leaching reactor vessel described above--is passed through a carbon adsorbing device. Fresh carbon is added periodically to the top of the device and loaded carbon removed from the bottom, and effluent from the carbon adsorption device is recycled to the washing or leaching stage.
It is the primary object of the present invention to provide for the effective removal of predetermined constituents from a particlized mineral material. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.